The optimal method for light grinding that I found is to do a combination chain of corpse flowers and the dragon in the crystal forge cave. You basically kill corpse flowers until you get to chain 4, 9, 14, 19, 24, and 29 then kill dragons every 5th, 10th, 15th, 20th, 25th, and 30th chain. This method is just like regular dragon light farming, but it's much faster because the corpse flowers are easier to kill. You mainly will get big chunks of light when you kill the dragon. It's still RNG-based, but I would say it's about 3 crystals an hour. This is how I got my weapon after leveling to 35.

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If you get an adapted dragon on chain 30, it will net you a gentle light if the game decides to give you light.